The United States is in the midst of an obesity epidemic, with nearly half of U.S. women of childbearing age being either overweight (BMI 25-29.9) or obese (BMI30). Obesity in this country reflects an ethnic disparity, with non- Hispanic black and Hispanic women disproportionately affected. Obese women are at particular risk to end their full-term pregnancies with unplanned cesarean delivery, in large part due to their abnormally slow labors. Obese women pregnant with their first babies (nulliparous women) are at the highest risk for unplanned cesarean delivery. When obese women have cesarean delivery, they are more likely than normal-weight women to experience significant post-cesarean morbidity and mortality. In vitro research investigating myometrial contractility suggests that the cellular metabolic milieu of obesity may account for the decreased contractile efficiency in labor, longer labor duration, and decreased response to commonly-used interventions to hasten labor that are clinically observed in obese populations. Gaps exist in our understanding of the correct timing and use of technological interventions in the labors of obese women. The proposed study will investigate the labor management of obese, nulliparous women to discover the practices associated with decreased risk of cesarean delivery. A Comparative Effectiveness approach will be used to describe and compare two different labor management models (obstetrician model vs. nurse-midwife model) against the outcome of cesarean delivery in a sample of obese, nulliparous women. Retrospective database analysis and detailed chart-review will be performed on the hospital records of obese, nulliparous women delivering at the University of Colorado Hospital, where approximately 40% of births are managed by nurse-midwives. Logistic regression and hazard analysis will be used to examine the differences in intervention use, intervention timing, and delivery outcomes between samples of obese, nulliparous women in the nurse-midwife vs. obstetrician models of labor care. Matched samples of obese women will be created via propensity score analysis. Biologic effect of obesity on women's response to exogenous oxytocin in labor will also be examined. The proposed research study and training plan are congruent with the applicant's long-term research goals to understand the biobehavioral determinants and effective intrapartum care management strategies for obese nulliparous women in order to decrease the incidence of cesarean delivery, its short and long-term adverse consequences, and the cost of healthcare for nulliparous childbearing women. Results obtained from this study will inform future research and promote new understanding of effective care practices for nurses, nurse- midwives, and physicians as they support the vulnerable population of obese, nulliparous women through labor to a safe birth outcome.